Degradation Of Refractory Organic Contaminants Research Articles

Enhanced activation of persulfate by bimetal and nitrogen co-doped biochar for efficient degradation of refractory organic contaminants: The role of the second metal

The leaching of metal ions limits the application of Fe-biochar catalyst in activating persulfate (PS). In this work, Fe-M (M = Co, Cu) and nitrogen co-doped biochar (Fe-M@N-BC) were synthesized through impregnating bio-waste soybean straw to activate PS for the removal of various refractory organic contaminants (tetracycline (TC), oxytetracycline (OTC), methyl orange (MO) and rhodamine B (RhB)). The catalysts were characterized by XRD, XPS, Raman, BET, TEM, SEM, and the degradation mechanism was investigated through quenching experiments and EPR. The results indicated that the doping of second metal (Co, Cu) has a strong promoting effect on catalytic activity with the order of Co > Cu. Surprisingly, the removal rates of TC, OTC, RhB, MO by Fe–Co@N-BC reached 84.7 %, 90.3 %, 89.4 %, and 91 %, respectively. The excellent catalytic performance of Fe–Co@N-BC was mainly attributed to abundant pyridinic-N, larger specific surface area (270 m2 g−1) and the Co(II)/Co(III) redox cycle promoting the regeneration of Fe(II). Notably, the formation of Co7Fe3 alloy could inhibit the leaching of iron ions and Fe–Co@N-BC possessed excellent reusability. Additionally, non-radical (1O2) was the main active species in the Fe–Co@N-BC/PS system. Finally, the degradation pathway of MO was proposed by HPLC-MS analysis. This research work provided an insight into how to reasonably utilize biological waste to construct highly efficient and stable catalysts for pollutants degradation.

Roles of B[sbnd]O[sbnd]Cu sites and graphite nitrogen on persulfate non-radical activation for tetracycline degradation

The activation of peroxymonosulfate (PMS) by carbon-based catalysts is deemed to be a promising method for the degradation of refractory organic contaminants in wastewater. Herein, a Cu-doping strategy in B and N co-doped carbon nanotubes with highly dispersed BOCu sites and graphite nitrogen were successfully synthesized for activating PMS to degradate tetracycline. The best removal rate of tetracycline within 60 min (97.63 %) was obtained by the 1.5 % Cu-BNC and the degradation rate was increased by 17.9 times. The enhanced catalyst activity was attributed to the promoting the cycle of the Cu(I)/Cu(II) redox pair by the formed BOCu sites, and the accelerating the electron transfer process by the adsorption of graphitic N for PMS. The non-free radical pathway including 1O2 and electron transfer played a dominant role in the 1.5 % Cu-BNC/PMS system. The degradation intermediates of TC were identified and three possible degradation pathways were proposed. Further toxicity analysis of the intermediates showed that the 1.5 % Cu-BNC/PMS system had a significant effect on weakening and reducing the biological toxicity and mutagenicity of TC. Moreover, it presented an excellent degradation performance in raw natural water. In general, the proposed regulation of carbon-based catalysts via the coordination-driven effect provides ideas for efficient wastewater treatment.

Linker regulation of iron-based MOFs for highly effective Fenton-like degradation of refractory organic contaminants

Iron-based MOFs with tunable structure, large surface area along with attractive diversity have been often used in heterogeneous Fenton-like reactions to generate hydroxyl groups for the degradation of new pollutants. It is unclear how linker substituents of MIL-101 with MTN-typed topology influence the heterogeneous Fenton. Solvothermal methods were used to successfully synthesize a series of MIL-101-X(Fe) with various substituents (X = -H, –NH2, –OH and –OCH3) in the side chains of organic ligands. Their physicochemical properties are fully investigated by various characterizations, which confirmed that changes in the substituents affected crystal morphology and thus catalytic efficiency. In the Fenton system, MIL-101-X showed significant differences in antibiotics removal. Particularly, the MIL-101-NH2 exhibited 100 % removal of SMX within 70 mins, with a rate of 30.06 times faster than MIL-101-H. This was related to the change in the active surface, following ligand functionalization, which greatly facilitates the dissociation of H2O2 and accelerates the iron cycling process. Therefore, this study provides the first mechanistic foresight on the regulation of Fenton-like reactions through modifying the substituents in the side chain of MOFs to alter their particle morphology and active surface.

Bicarbonate enhanced heterogeneous activation of peroxymonosulfate by copper ferrite nanoparticles for the efficient degradation of refractory organic contaminants in water

Nowadays, the treatment of residual refractory organic contaminants (ROCs) is a huge challenge for environmental remediation. In this study, a potential process is provided by copper ferrite catalyst (CuFe2O4) activated peroxymonosulfate (PMS, HSO5−) in the bicarbonate (HCO3−) enhanced system for efficient removal of Acid Orange 7 (AO7), 2,4-dichlorophenol, phenol and methyl orange (MO) in water. The impact of key reaction parameters, water quality components, main reactive oxygen species (ROS), probable degradation mechanism, rational degradation pathways and catalyst stability were systematically investigated. A 95.0% AO7 (C0 = 100 mg L−1) removal was achieved at initial pH (pH0) of 5.9 ± 0.1 (natural pH), CuFe2O4 dosage of 0.15 g L−1, PMS concentration of 0.98 mM, HCO3− concentration of 2 mM, and reaction time of 30 min. Both sulfate radical (SO4−•) and hydroxyl radical (•OH) on the surface of catalyst were proved as the predominant radical species through radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The buffer nature of HCO3− was partially contributed for the enhanced degradation of AO7 under CuFe2O4/PMS/HCO3− system. Importantly, according to 13C nuclear magnetic resonance (NMR) and EPR analysis, the positive effect of bicarbonate may be mainly attributed to the formation of peroxymonocarbonate (HCO4−), which may enhance the generation of •OH. The magnetic CuFe2O4 particles can be well recycled and the leaching concentration of Cu was acceptable (<1 mg L−1). Considering the widespread presence of bicarbonate in water environment, this work may provide a safe, efficient, and sustainable technique for the elimination of ROCs from practical complex wastewater.

Efficient activation of peroxymonosulfate mediated by Co(II)-CeO2 as a novel heterogeneous catalyst for the degradation of refractory organic contaminants: Degradation pathway, mechanism and toxicity assessment

A series of Co(II)-CeO2 mixed metal oxides were synthesized by a facile hydrothermal-calcination procedure for activating peroxymonosulfate (PMS) and degrading toxic and difficult biodegradable organics. Co(II)-CeO2 showed excellent degradation performance toward rhodamine B (RhB), toluidine blue, methylene blue and diclofenac. RhB is a refractory organic contaminant, and ecotoxicological evaluation unraveled its harmfulness to the biosphere. RhB was selected as the model pollutant to investigate catalytic mechanisms. Parameters affecting degradation performance were profoundly investigated, including Co:Ce feed ratio, initial pH, PMS dosage, catalyst dosage, RhB concentration, coexisting ions and reaction temperature. Reaction mechanisms were proposed based on density functional theory calculations and identifications of reactive oxygen species. Improvements have been achieved in seven aspects compared to previous studies, including 100% degradation ratio in both real water samples and each reuse of the catalyst, ultrafast degradation rate, cost-effectiveness of the catalyst, toxicity-attenuation provided by the developed degradation method, high degree of mineralization for the model pollutant, negligible leaching of active sites, and the enhancement of catalytic performance by utilizing trace leached cobalt, endowing the technique with broad applicability and prospect.

Magnetic Co/Fe nanocomposites derived from ferric sludge as an efficient peroxymonosulfate catalyst for ciprofloxacin degradation

• Cobalt adsorbed on ferric sludge was recycled to create bimetallic catalyst via a facile solvothermal method. • Co/Fe nanocomposites derived from ferric sludge (CoFe@FS) exhibited an excellent performance toward PMS. • SO 4 •− , • OH, O 2 •− and 1 O 2 were produced from PMS activation by synergetic effect of Co and Fe on the catalyst surface. • The possible degradation mechanism of CIP is proposed based on DFT calculations and LC/MS analyses. • This is a cost-effective method to achieve “treating wastewater by waste residuals”. Ferric sludge, generated during drinking water purification process, can be considered as a promising support with potential iron resource. Herein, magnetic bimetallic Co/Fe nanocomposite derived from ferric sludge (CoFe@FS) was created via a facile solvothermal treatment and employed as an efficient peroxymonosulfate (PMS) activator for the elimination of antibiotic ciprofloxacin (CIP) in water. CoFe@FS exhibited nano-sphere structure with the composites of CoO, CoFe 2 O 4 and SiO 2 crystals and presented excellent catalytic performance with 97.3% removal efficiency of 10 mg/L CIP within 15 min. Sulfate radicals (SO 4 •− ), hydroxyl radicals ( • OH) superoxide radicals (O 2 •− ) and singlet oxygen ( 1 O 2 ) all contributed to CIP degradation, and SO 4 •− functioned as the dominant reactive species in this activation system. CoFe@FS composite exhibited great reusability due to the strong Co/Fe-Si interaction and was able to regenerate by a simple solvothermal process. The CIP degradation mechanism in the CoFe@FS/PMS system were also proposed based on density functional theory (DFT) calculations and analysis of intermediate products. Overall, the magnetic Co/Fe bimetallic catalyst derived from ferric sludge could be employed as high-efficiency and low-cost candidate for the degradation of refractory organic contaminants. This work not only provides a promising reclamation strategy of water treatment waste from ferric sludge to high-effective catalyst, but also clarifies the mechanisms of PMS activation and CIP degradation. The more stable bimetallic CoFe catalysts derived from waste sludge need to be developed in the future study to relieve the occurrence of metal leaching.

Enhanced electro-peroxymonosulfate activation using a carbon nanotube filter with a functionalized polyelectrolyte

An innovative electroactive membrane was designed with polyelectrolyte modification for electro-PMS activation and degradation of refractory organic contaminants in a flow-through filtration model.

Recent advances in persulfate-based advanced oxidation processes for organic wastewater treatment

In recent years, with the emergence of new pollutants, the effective treatment of wastewater has become very important. Persulfate-based advanced oxidation processes have been successfully applied to the treatment of wastewater, such as wastewater containing antibiotics, pharmaceuticals and personal care products, dyes, endocrine-disrupting chemicals, chlorinated organic pollutants, and phenolics, for the degradation of refractory organic contaminants. This paper summarizes the production of sulfate radicals, which can be generated by the activation of persulfate via conventional and emerging approaches. The existing problems of persulfate-based advanced oxidation processes were analyzed in detail, including residual sulfates, coexisting factors (coexisting inorganic anions and natural organic matter), and energy consumption. This paper proposes corresponding possible solutions to the problems mentioned above, and this paper could provide a reference for the application of persulfate-based advanced oxidation processes in actual wastewater treatment.

Degradation of saccharin by UV/H2O2 and UV/PS processes: A comparative study

Artificial sweeteners have raised emerging concern due to their potential threats to human health, which were frequently detected in aquatic environment with median concentrations. Although current researches have widely reported that ultraviolet light-activated persulfate process (UV/PS) was superior to UV/H2O2 process for the degradation of refractory organic contaminants, UV/H2O2 process presented a more satisfactory saccharin (SAC) removal efficiency than UV/PS process, completely degraded 20 mg/L SAC within 45 min. Hence, quenching and probe experiments were employed to investigate the difference between hydroxyl radical (OH)- and sulfate radical (SO4-)-mediated oxidation mechanisms, which revealed the higher reactivity of OH (1.37–1.56 × 109 M−1 s−1) toward SAC than SO4- (3.84–4.13 × 108 M−1 s−1). A combination of density functional theory calculation and transformation products identification disclosed that OH preferred to attack the benzene ring of SAC via hydrogen atom transfer pathway, whereas SO4- oxidation was conducive to the cleavage of -C-NH2 bond. Increasing oxidant concentration significantly accelerated SAC degradation in both processes, while UV/H2O2 process consumed lower electrical energy with respect to UV/PS process. Additionally, UV/H2O2 system presented excellent adaptability and stability under various water matrices parameters (e.g. pH, anions and humic acid). While both UV/H2O2 and UV/PS processes promoted the generation of disinfection by-products (DBPs) during subsequent chlorination, and prolonging pretreatment time posed positive effect on reducing the formation of DBPs. Overall, the results clearly demonstrate the high efficiency, economy and practicality of UV/H2O2 process in the remediation of SAC-contaminated water.

Efficient degradation of ibuprofen by electro-Fenton with microtubular gas- diffusion electrodes synthesized by wet-spinning method

• A novel microtubular gas diffusion electrode (MGDE) was fabricated and tested. • Characterized by physical methods in structural characteristics electrochemical performance. • The pH value has little effect on H 2 O 2 production, the current efficiency is 42.8%. • Efficient ibuprofen degradation in electro-Fenton system with MGDEs was optimized. Gas-diffusion electrodes (GDEs) are the efficient generator for the hydrogen peroxide, which plays an important role in the degradation of refractory organic contaminants by electro-Fenton processes. In this work, the microtubular gas-diffusion electrodes (MGDEs) were fabricated with the carbon nanotubes (CNTs) hollow fiber base by wet-spinning technology and then employed as gas-diffusion electrodes (GDEs). Characterized by FESEM, TEM, BET, XPS, the MGDEs were proved to be relatively compact and intact without fracture on the hollow fiber surface. Cyclic voltammetry test in three electrodes system was carried out to prove the catalysis effect of the surface functional groups in the electrochemical reactions. The time-course of H 2 O 2 production rate in the range of the different current density (10 ~ 25 mA cm −2 ), pH value (3.0 ~ 9.0) and electrolyte concentration (0.01 ~ 0.1 M Na 2 SO 4 ) were conducted to evaluated the electrochemical performance of MGDEs and explorer the optimal condition. The stability of electrocatalytic was also tested by repeated runs. Furthermore, several parallel-degradation process of the simulated wastewater with the 1.0 ~ 10.0 mg L -1 IBP were carried out in electro-Fenton system. Under the optimal conditions, the removal rate of IBP could reach 90.2% in 120 min with the pseudo first-order degradation rate constant of 0.01415 min −1 . It shows the potential of this system to degrade NSAIDs.

Highly dispersed iron-doped biochar derived from sawdust for Fenton-like degradation of toxic dyes

Wastewater pollution is a global challenge in the field of environmental remediation. Functional biochar as Fenton-like catalyst receives growing attention for degradation of refractory organic contaminants in wastewater. This work provides a step-forward to develop effective functional biochar via revealing the mechanism of surface catalysis. The synthesis of iron-doped biochar (Fe@BC) was conducted through iron impregnation and carbonization of waste sawdust. Highly dispersed iron species on graphitic biochar is verified by multi-techniques including electron probe microanalyzer, transmission electron microscope, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrum and Raman spectrum. Rhodamine B (RhB) degradation above 92.7% is obtained within 140 min. Surface catalysis for generating hydroxyl radical is proved by iron determination, radical identification, and catalyst characterizations. Effective degradation of binary dyes is achieved. Fe@BC is an excellent catalyst with broad operation pH and highly stability. Promising application of the functional biochar provides a sustainable and ecofriendly strategy for wastewater treatment.

Implications for practical application of commercial reduced iron powders to activate aqueous sulfite for decontamination of organics

Sulfate radicals (SO4•−) based advanced oxidation processes (AOPs), with high efficiency and selectivity toward degradation of refractory organic contaminants, have captured increasing worldwide attention. Here, an efficient advanced oxidation process based on SO4•− (i.e., a CRI/S(IV) process), induced by commercial reduced iron (CRI) powder-induced aqueous sulfite [S(IV)] activation for favorable degradation of refractory organics, is reported. The CRI/S(IV) coupled system efficiently decomposes rhodamine B (RhB) and 4-chlorophenol (4-CP) at weakly acidic and even neutral pHs. The distributions of active sulfur and iron species distribution in the CRI/S(IV) system were investigated and implied that HSO3−, FeHSO3+ and FeSO3+ were the main active species for S(IV), Fe(II), and Fe(III), respectively. In addition, radical quenching experiments show that both SO4•− and hydroxyl radicals (•OH) are present in this CRI/S(IV) system with SO4•− as the dominant reactive radical for contamination removal. Furthermore, this novel process surpassed both CRI/Oxone and CRI/persulfate systems towards the organic degradation. This work might provide an implication for an efficient practical route for SO4•− activation for wastewater decontamination, particularly for sulfite contaminated wastewaters with recalcitrant organic contaminants.

Enhanced heterogeneous Fenton-like degradation of refractory organic contaminants over Cu doped (Mg,Ni)(Fe,Al)2O4 synthesized from laterite nickel ore

The heterogeneous Fenton-like catalyst (Mg,Cu,Ni)(Fe,Al)2O4 was synthesized via a coprecipitation method using laterite nickel ore leaching solution as raw material. The effects of CuCl2·2H2O addition and calcination temperature on the microstructures and degradation properties of the obtained products were investigated. Results showed that higher calcination temperature could promote the migration of Cu2+ ions from CuO to the spinel ferrite lattice and occupied octahedral sites. The degradation efficiencies (η) of various types of low-concentration dyes and tetracycline were higher than 95%, which was mainly due to the accelerated generation of OH radicals by the synergistic effect of Fe3+ and Cu2+ ions in octahedral sites of the formed (Mg,Cu,Ni)(Fe,Al)2O4. Moreover, after five consecutive degradation cycles, the η of RhB was still close to 100%, TOC removal efficiency was maintained around 40% and the concentrations of metallic ions in degraded solutions were all lower than the national effluent discharge standard (GB8978-1996), confirming the as-obtained (Mg,Cu,Ni)(Fe,Al)2O4 was an eco-friendly heterogeneous Fenton-like catalyst with excellent stability and reusability. This study may provide an effective reference for large scale preparing efficient heterogeneous Fenton-like catalysts from natural minerals in treating the wastewater contaminated by refractory organics.

Transformation from a non-radical to a radical pathway via the amorphization of a Ni(OH)2 catalyst as a peroxymonosulfate activator for the ultrafast degradation of organic pollutants.

The peroxymonosulfate (PMS) activation reaction using transition-metal-based catalysts has been proven to be a promising approach for the degradation of refractory organic contaminants; however, the ambiguous structure-property relationship between the intrinsic free-radical and non-radical mechanistic pathway selectivity and structural characteristics greatly hinders the development of active catalysts. Taking Ni(OH)2 as a model catalyst, this work reveals that the pathway selectivity during PMS activation can be controlled via the construction of crystalline and amorphous structures. Electron paramagnetic resonance and radical quenching experiments verified that amorphous Ni(OH)2 with disordered -OH, synthesized via a formamide-assisted precipitation method, dramatically promotes the generation of ˙OH and SO4˙- (the radical pathway), which highly improved the degradation efficiencies toward organic contaminants. However, crystalline Ni(OH)2 was found to activate PMS through via a non-radical pathway. Density functional theory calculations reveal that amorphous Ni(OH)2 possesses an electron-rich active surface, which favors the breaking of O-O bonds instead of O-H bonds in PMS molecules and triggers radical production. As confirmed via electrochemical measurements, the essence of PMS activation was uncovered; it was found that pathway selectivity was determined based on the electron-donating capabilities, which were highly dependent on the -OH group environments. Impressively, the catalytic mechanism of the same material can be successfully and precisely regulated from a non-radical to a radical pathway for PMS activation via a structural engineering method, which can simultaneously improve the catalytic performance for the effective elimination of emerging contaminants in aquatic environments.

Ionothermal Carbonization of Biomass to Construct Fe, N-Doped Biochar with Prominent Activity and Recyclability as Cathodic Catalysts in Heterogeneous Electro-Fenton

Heterogeneous electro-Fenton is an efficient advanced oxidation process for the degradation of refractory organic contaminants in wastewater, and its efficiency is governed by cathodic catalysts. I...

Catalytic activation of O2 by Al0-CNTs-Cu2O composite for Fenton-like degradation of sulfamerazine antibiotic at wide pH range

In this study, a novel Al°-CNTs-Cu2O composite, capable of activating O2 to generate H2O2 and further to reactive oxygen species (ROSs) at a wide pH range, was synthetized, characterized and applied for the degradation of sulfamerazine. In the activation of O2 by Al°-CNTs-Cu2O composite, H2O2 was generated from the reaction of O2 with Al°-CNTs, which could be catalytically decomposed into O2− and OH by Cu2O, the formed Cu(II) could be rapidly reduced to Cu2O by Al°-CNTs in composite, which made Al°-CNTs-Cu2O composite reusable and decreased the leaching of copper ions into solution. The removal efficiency of SMR and TOC was 73.91 % and 56.80 %, respectively at initial pH = 5.8, T = 20 °C, O2 flow rate = 100 mL/min, Al°-CNTs-Cu2O dosage = 2 g/L, SMR = 50 mg/L, and reaction time = 60 min. The removal efficiency of SMR kept almost unchanged and the concentration of copper ions in solution was below 0.5 mg/L. The Al°-CNTs-Cu2O/O2 process could be used as a novel catalyst for the degradation of refractory organic contaminants in water and wastewater by Fenton-like process at a wide pH range through the in situ generation of H2O2.

A novel in-situ chemical oxidation channel – Selective pH-dependence of refractory β-lactam antibiotics in the synergistic mechanism of persulfate and g-C3N4 under visible light

The degradation characteristics of four typical structures of β-lactam antibiotics were studied during the synergistic oxidation mechanism of persulfate (PS) and mesoporous g-C3N4 (MCN) under visible light irradiation including amoxicillin (AMX), cefotaxime (CFX), meropenem (MER), and sulbactam (SUL). Notably, the degradation of SUL in the MCN/PS system exhibits a pH-dependence different from the other three antibiotics. In this work, a novel oxidation channel for such persistent organic pollutant was revealed. Initially, SUL was bound specifically with PS via the addition reaction caused by the electron transfer between the oxygen atoms of the sulfoxide group of SUL and the HSO3− group generated by the protonation of PS. The reaction was carried out under acidic conditions and generated the SUL-O-SO2H byproducts. Successively, the adduct was further oxidized by the free radicals and singlet oxygen until the intermediate products were completely mineralized. The environmental factors of the reaction, such as the presence of humic acid and the cation-anion interactions, were also considered. In this work, the degradation pathways of SUL, the hydrolysis of the β-lactam ring, the decarboxylation, and the deamination reaction based on the combination of DFT calculations and the HPLC-QTOF-MS/MS analysis are elucidated. The toxicity of the byproducts was also calculated via the USEPA TEST. The findings improve the understanding of the reaction mechanism of the persulfate and the photocatalytic systems and provide new ideas for the oxidative degradation of refractory organic contaminants.

Superfast degradation of refractory organic contaminants by ozone activated with thiosulfate: Efficiency and mechanisms

Thiosulfate (S2O32-) is frequently used as an ozone (O3) quenching agent when investigating the ozonation of organic contaminants and the kinetics thereof. In this study, however, O3 is activated by S2O32-, resulting in a superfast degradation of O3-refractory contaminants. Therefore, the focus of this study is the exploration into the enhancing role of S2O32- in the degradation of refractory organic contaminants by O3, which has been overlooked thus far. Results obtained from scavenging experiments and electron paramagnetic resonance (EPR) spectra verify that •OH generated from the reaction of S2O32- with O3 is mainly responsible for the superfast degradation of O3-refractory contaminants. The •OH yield from the O3/S2O32- process is determined to be 0.216. A plausible mechanism for the generation of •OH from the O3/S2O32- process is proposed with the implementation of density functional theory (DFT). Initially, ozone reacts with a sulfur of S2O32- to form OOOSSO32-. The adduct then rearranges to OO(O)SSO32- or HOO(O)SSO32- in the presence of H+, which cleaves to give a sulfoxide radical cation and O2•-/HO2•. O2•-/HO2• is rapidly transformed into •OH by O3 through a series of steps. Degradation efficiency of O3-refractory contaminants of this process highly depends on the molar ratio of S2O32- and O3 ([S2O32-]:[O3]). The optimal [S2O32-]:[O3] is pH dependent in synthetic water (e.g. 0.3 at pH 7). The presence of bicarbonate inhibits the degradation of refractory contaminants by the O3/S2O32- process. Humic acid exhibits a slight enhancing effect at low concentrations (0.1–0.2 mg-C/L), and an inhibiting effect at higher concentrations (≥0.4 mg-C/L). In addition, the efficacy of the O3/S2O32- process in real water matrices is also confirmed.

Remediation of persistent organic pollutants in aqueous systems by electrochemical activation of persulfates: A review

Sulfate-radical-based advanced oxidation processes (SR-AOPs) have been widely applied in environmental remediation during the past decade, especially in the degradation of refractory organic contaminants. The electrochemical method, which is considered as one of the most efficient ways to generate sulfate radical, has been extensively investigated for the activation of persulfate recently. This work presented a thorough assessment towards the performance of electrochemically activated persulfate for the removal of persistent organic pollutants (POPs) in aqueous systems. The mechanism and superiority of electrochemically activated persulfates were revealed accordingly. Some major factors (e.g., electrode material, pH, current density, and persulfate concentration) influencing the electrochemical activation of persulfates to remove POPs were also discussed. Considering the increasing quantity of publications on this subject, it is significant to broader guidelines such as the efficiency for practical application, quantization of organic by-products, and cost-effectiveness of the electrochemical method to optimize active persulfate in the water treatment processes.

Activation of peroxymonosulfate by magnetic Co-Fe/SiO2 layered catalyst derived from iron sludge for ciprofloxacin degradation

Drinking water treatment sludge provides the iron resource and a promising support to create bimetallic composites. In this work, a magnetic Co-Fe/SiO2 layered catalyst (LC) was synthesized by a facile hydrothermal method and used as an effective peroxymonosulfate (PMS) activator to degrade ciprofloxacin (CIP), a typical refractory antibiotic agent contaminant. Co-Fe/SiO2 LC exhibited superior catalytic performance with 98% CIP degradation efficiency in 10 min compared to other Co/Fe monometallic oxides and ions. The catalyst had great potential for practical application under various conditions. A synergistic effect between solid Co and Fe occurred on the surface of the catalyst due to the accelerated reduction of Co3+ by Fe2+. Both sulfate radicals (SO4•−) and hydroxyl radicals (•OH) were produced in the PMS activation process, and SO4•− contributed to much more CIP degradation. Based on kinetic models, the CIP degradation at different catalyst loadings could be well predicted. The catalyst showed excellent stability and reusability due to the strong Co/Fe-O and Co/Fe-Si interaction. This work provided a promising iron sludge reuse method to convert the “waste sludge” to a high-efficiency and low-cost bimetallic catalyst for the degradation of refractory organic contaminants in aquatic environments.